A factory using industrial robots is generally equipped with many apparatuses requiring a large amount of electric power, and thus the probability of the occurence of a power failure therein is high. Once a power failure occurs, the operation of the robots cannot be restarted in the same state as before, even if an electric power has been again supplied thereto, and thus the operator must carry out the procedures necessary for restarting the operation thereof. Consequently, when many industrial robots are used in a large manufacturing line, the restarting of the operation of the robots takes a long time, which causes a problem in the management of the factory.
To simply restart the operation, there is used a method of saving the data of a task processed by a processor, at predetermined intervals, in a non-volatile memory or the like. More specifically, when a power failure occurs, the data saved in the non-volatile memory is read out and the processing state when the power failure occurred is restored, and thus the operation of a robot can be restarted in the same state as before.
Nevertheless, when a robot is controlled by a complex method, the number of data to be saved is increased and the data must be saved at very short intervals, and thus the load on a processor is increased. When the intervals at which the data is saved are increased, a time lag between a time at which data is saved and a time at which a power failure occurs is also increased, and thus the robot cannot be correctly restarted in the same state as before.